The chemical effects of high-intensity ultrasound on alkane solutions are reported. Primary products are H2, CH4, C2H2, and smaller 1-alkenes. Strong similarities to high-temperature (>1200°C) alkane pyrolysis are observed and a radical chain mechansim is proposed. The principal sonochemical process appears to be C-C bond cleavage with secondary abstractions and rearrangements. In order to probe the factors which affect sonochemical yields, we have used two very different chemical dosimeters in alkane solutions: radical trapping by diphenylpicrylhydrazyl and decomposition of Fe(CO)5. In both cases, good correlation is found between the log of the sonochemical rate and the solvent vapor pressure. This result is justifiable in terms of the cavitation "hot-spot" explanation of sonochemistry. Thus, decreasing solvent vapor pressure increases the intensity of cavitational collapse, the peak temperature reached during such collapse, and, consequently, the rates of sonochemical reactions.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry